IWM doesn't recognise 800k drive

[RickNel]

I have an 800k Sony drive that has stopped booting on a 512k or a Plus, but still reads\writes OK when attached to my IIsi. The IIsi has SWIM chip, the Compacts have the IWM chip. But I understand that the SWIM is just a combination of the IWM with another set of logic to drive the 1.4mb diskettes, known as the Sander logic, and it selects which path to use according to the diskette ID information. So the SWIM chip is controlling the drive using exactly the same logic as the IWMs should do. Both Compact logic board are using the Plus 128k ROMs, and both have booted with this drive in the past.

I can't work out what signal the IWM is not getting. The drive's onboard logic seems to be OK, because it works in the IIsi. There are a couple of small caps on the drive's logic board. I suppose it is possible some signal is just weaker than the IWM is calibrated for? The data read signal would seem to be the main candidate. Is there any known issue like this?

Rick

 

[uniserver]

I bet the Head tension spring needs to be adjusted to one notch tighter.

also have you tried another boot disk?

Reading and writing is one thing,

Booting is another.

 

[uniserver]

Don't you hate it when you get so technically involved into something, then somebody just swoops in posts something so remedial.

Not that what I suggested will fix it, but I have had funky issues like what you are having with a Dual Drive 800k se, one of the drives would boot, one would not, however once booted both of the drives would R/W to disks.

I took the the one that was not booting cleaned it up, and kicked the tension on the adjustable perch(in the head assembly), just like CC_333 and I have talked about before, and bam they both would boot flawlessly. Its a shame though, ended up replacing those drives with superdrives and making the main board into a FDHD one.

Charles

 

[onlyonemac]

I've also heard that muddling up red-striped and yellow-striped cables is a problem. One is for 400k drives and the other for 800k drives. I'm not sure which goes with which, but try swapping the cables. That might help.

 

[RickNel]

If the problem is mechanical, I will be relieved - so I'll putz around with the head pressure for a while and see if I get a resolution. Remember this drive reads and writes to one logic board, but not to two others. I suppose its possible the MacII series SWIM chips run to a slightly more tolerant read signal or put more current through the buffers somewhere.

My worry was that some electronic component on the drive itself might have failed or gone off spec, weakening the signal. I've ordered a schematic for the Sony 880k drive from Bomarc, but last I heard he was still burrowing through a snowdrift in Wyoming trying to get to the post office. :-/

 

[uniserver]

yes but does it boot... on others? my guess is no.

 

[techknight]

Did i read your post correctly? you hooked the drive up to your IIsi and its fine? but not in the compact? the bourns filter is to blame if this is the case

 

[RickNel]

@Technight read correctly. Sounds promising!

'Scuse my ignorance, but where do I locate the bourns filter you refer to? Is it swappable? I don't yet have the schematics to hand.

Rick

 

[techknight]

behind the internal floppy connector and just ahead of the external floppy connector. Clip it out. this will kill the external floppy from ever being used, but it will restore the internal drive operation if this is bad.

 

[uniserver]

that is great information techkinght! thanks!

 

[RickNel]

I'll try it, but I'll desolder the chip in case I can find or make a replacement later. Thanks.

Rick

 

[RickNel]

Well I did desolder the Bourns filter behind the floppy connector, but it hasn't solved the problem. In fact it seems to have added another problem, because the disk no longer spins up. On power-up, the drive does its self-alignment by seeking Track 0. The floppy request icon comes up, but with any floppy inserted the icon alternates between floppy request (the question mark) and floppy bad (the X on the floppy icon). Also the servo eject does not occur, though I hear that servo motor clicking as if it is receiving single-step instructions but not moving anything. It will sometimes run the eject sequence after I press the eject button on the 800k drive itself. So it seems commands are not reaching the drive, including the motor on command. I'll look for a source for replacement filters or make them if necessary, but their might be some other problem as well.

I'm going to have to trace this out more thoroughly to see where the signals go between the floppy port and the IWM chip. I hope schematics are in the mail. Can't find anything in the Pina books that gets down to this level on drive issues.

Rick

 

[techknight]

The drive is attempting to do something, therefore the IWM is fine. Sounds like voltage sag to me.

 

[RickNel]

Yes, I've confirmed the IWM works fine and system will boot from a Superdrive (Sony MFD-75W) on the internal connector (with pin 9 of the cable disconnected - I put in a DIP switch for testing ). I've replaced the Bourns filter with a new one.

So how do I follow up on "voltage sag" and why would that affect MFD-51W but not MFD-75 drive?

I haven't found any guide to thorough checkout of this type of drive. I've been through all the stages of cleaning and lubrication.

I am wondering whether alignment might have got affected somehow, and how I can check/adjust alignment (I've done it often enough with 5.25" drives on older systems).

Rick